The chiral tridentate spiro P‐N‐S ligands (SpiroSAP) were developed, and their iridium complexes were prepared. Introduction of a 1,3‐dithiane moiety into the ligand resulted in a highly efficient chiraliridium catalyst for asymmetrichydrogenation of β‐alkyl‐β‐ketoesters, producing chiralβ‐alkyl‐β‐hydroxyesters with excellent enantioselectivities (95–99.9 % ee) and turnover numbers of up to 355 000